[Numpy-discussion] suggested change of behavior for interp

Benjamin Root ben.root@ou....
Tue Jun 4 21:15:21 CDT 2013


Could non-monotonicity be detected as part of the interp process? Perhaps a
sign switch in the deltas?

I have been bitten by this problem too.

Cheers!
Ben Root

On Jun 4, 2013 9:08 PM, "Eric Firing" <efiring@hawaii.edu> wrote:
>
> On 2013/06/04 2:05 PM, Charles R Harris wrote:
> >
> >
> > On Tue, Jun 4, 2013 at 12:07 PM, Slavin, Jonathan
> > <jslavin@cfa.harvard.edu <mailto:jslavin@cfa.harvard.edu>> wrote:
> >
> >     Hi,
> >
> >     I would like to suggest that the behavior of numpy.interp be changed
> >     regarding treatment of situations in which the x-coordinates are not
> >     monotonically increasing.  Specifically, it seems to me that interp
> >     should work correctly when the x-coordinate is decreasing
> >     monotonically.  Clearly it cannot work if the x-coordinate is not
> >     monotonic, but in that case it should raise an exception.  Currently
> >     if x is not increasing it simply silently fails, providing incorrect
> >     values.  This fix could be as simple as a monotonicity test and
> >     inversion if necessary (plus a raise statement for non-monotonic
cases).
> >
> >
> > Seems reasonable, although it might add a bit of execution time.
>
> The monotonicity test should be an option if it is available at all;
> when interpolating a small number of points from a large pair of arrays,
> the single sweep through the whole array could dominate the execution
> time.  Checking for increasing versus decreasing, in contrast, can be
> done fast, so handling the decreasing case transparently is reasonable.
>
> Eric
>
> >
> > Chuck
>
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